It is known that mouse strains differ in their susceptibility to corticosteroid-induced cleft palate. It has also been shown that this variation in corticosteroid (CORT) responsiveness is related to genetic variation in loci at or near the major histocompatibility complex (MHC, H-2 in mice). We have demonstrated that H-2 haplotype differences are sufficient to alter CORT-induced susceptibility to cleft palate and temporal changes in normal long maturation. Our new data indicates that the mechanism for these haplotype-specific differences in CORT responsiveness is likely related to factors modulating the expression of the glucocorticoid receptor (GR), which is encoded outside the H-2 genomic region. We have designed a series of Specific Aims using the well characterized H-2 congenic mouse model and immunochemical, biochemical and molecular methodologies to test the hypothesis that H-2 associated modulation of GR expression and/or function is a key molecular mechanism regulating CORT responsiveness and, hence, CORT- induced cleft palate. Aim 1. GR translational and post-translational regulation: to analyze haplotype-specific qualitative and quantitative variation in GR characteristics and pattern of in situ spatial distribution with progressive development among H-2 congenic mice. Aim 2. GR transcriptional regulation: to compare haplotype-specific differences in the steady state levels, developmental expression, and in situ spatiotemporal localization of GR mRNA among H-2 congenic strains with progressive development. Aim 3. GR function analysis: to delineate the mechanism of H-2 associated differences in GR function among H-2 congenic mice by comparing haplotype-specific variation in (a) ligand-GR binding to a specific high affinity GRE DNA (GR-GRE binding), and (b) mRNA expression and spatial distribution of four developmentally expressed "CORT-responsive" genes (EGF, TGF-beta1, TGF- beta2, TGF-beta3) in the presence of exogenous CORT. The demonstration of haplotype-specific variation in GR expression and CORT respons- iveness will support the hypothesis that the H-2 complex contains genetic information encoding trans-acting factors which regulate GR expression and/or function. We will then pursue gene mapping and cloning studies to identify the glucocorticoid responsiveness gene locus (GRG) at or near the H-2 complex on mouse chromosome 17, subsequently human homologs.